Rigid, or semirigid, thermoplastic beverage containers have been known for many years. One example of such containers are high density polyethylene milk containers that have a capacity of a quart, a gallon or other common sizes. These containers typically comprise high density polyethylene. High density polyethylene is made from an ethylene stream using a Ziegler-Natta catalyst in either liquid phase or gas phase processes. Other vinyl polymers, can also be used in formulating these beverage containers including polymers made from such monomers including ethylene, propylene, butylene, butadiene, styrene and others. Such materials often contain small concentrations of residual monomers, contaminants in the olefin feed, catalyst residues and other contaminants. Such containers are typically blow molded using common thermoforming technology to shape a preform into a finished bottle or container.
Biaxially oriented blow molded thermoformed polyester beverage containers are disclosed in J. Agranoff (Ed) Modern Plastics, Encyclopedia, Vol. 16, No. 10A, P. (84) pp. 192-194. These beverage containers are typically made from a polyester material. Such polyesters are commonly made from a diol such as ethylene glycol, 1,4-butane diol, 1,4-cyclohexane diol and other diols copolymerized with an organic diacid compound or lower diester thereof such as terephthalic acid, 2,6-naphthalene dicarboxylic acid etc. The condensation/polymerization reaction occurs between the dicarboxylic acid, or a dimethyl ester thereof and the glycol material in a heat driven reaction that releases water or methanol as a reaction by-product leaving the high molecular weight polyester material. Typically, bulk polyester is injection blow molded over a steel-core rod or are formed into a preform containing the polyester. The preform is introduced into a blow molding machine wherein the polyester is heated and blown to an appropriate shape and volume for a beverage container the preform can be a single layer material, can be a bilayer or multilayer preform. Such preforms can form bilayer or multilayer bottles.
The thermoplastic polyester is a high molecular weight material, but can contain a large variety of relatively low molecular weight compound, substantially less than 500 grams per mole. These compounds can be extractable into beverage within the container. These beverage extractable materials typically comprise impurities in feed streams of the diol or diacid used in making the polyester. Further, the extractable materials can comprise degradation by-products of the polymerization reaction, the preform molding process or the thermoforming blow molding process. Further, the extractable materials can contain residual diester, diol or diacid materials including methanol, ethylene glycol, terephthalic acid, dimethyl terephthalic, 2,6-naphthalene dicarboxylic acid and esters or ethers thereof. Relatively low molecular weight oligomeric linear or cyclic diesters, triesters or higher esters made by reacting one mole of ethylene glycol with one mole of terephthalic acid may be present. These relatively low molecular oligomers can comprise two or more moles of diol combined with two or more moles of diacid. Schiono, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 17, pp. 4123-4127 (1979), John Wiley & Sons, Inc. discusses the separation and identification of PET impurities comprising poly(ethylene terephthalate) oligomers by gel permeation chromatography. Bartl et al., "Supercritical Fluid Extraction and Chromatography for the Determination of oligomers and Poly(ethylene terephthalate) Films", Analytical Chemistry, Vol. 63, No. 20, Oct. 15, 1991, pp. 2371-2377, discusses experimental supercritical fluid procedures for separation and identification of a lower oligomer impurity from polyethylene terephthalate films.
Beverages containing these soluble/extractables, when consumed by the public, can exhibit an off-taste, a changed taste or even, in some cases, reduced taste due to the presence of extractable compounds. The extractable compounds can add to or interfere with the perception of either the aroma note or flavor notes from the beverage material. Additionally, some substantial concern exists with respect to the toxicity or carcinogenicity of any organic material that can be extracted into beverages for human consumption.
The technology relating to compositions used in the manufacture of beverage containers is rich and varied. In large part, the technology is related to coated and uncoated polyolefin containers and to coated and uncoated polyester that reduce the permeability of gases such as carbon dioxide increasing shelf life. The art also relates to manufacturing methods and to bottle shape and bottom configuration. Deaf et al., U.S. Pat. No. 5,330,808 teach the addition of a fluoroelastomer to a polyolefin bottle to introduce a glossy surface onto the bottle. Visioli et al., U.S. Pat. No. 5,350,788 teach methods for reducing odors in recycled plastics. Visioli et al. disclose the use of nitrogen compounds including polyalkylenimine and polyethylenimine to act as odor scavengers in polyethylene materials containing a large proportion of recycled polymer.
Wyeth et al., U.S. Pat. No. 3,733,309 show a blow molding machine that forms a layer of polyester that is blown in a blow mold. Addleman, U.S. Pat. No. 4,127,633 teaches polyethylene terephthalate preforms which are heated and coated with a polyvinylidene chloride copolymer latex that forms a vapor or gas barrier. Halek et al., U.S. Pat. No. 4,223,128 teaches a process for preparing polyethylene terephthalate polymers useful in beverage containers. Bonnebat et al., U.S. Pat. No. 4,385,089 teaches a process for preparing biaxially oriented hollow thermoplastic shaped articles in bottles using a biaxial draw and blow molding technique. A preform is blow molded and then maintained in contact with hot walls of a mold to at least partially reduce internal residual stresses in the preform. The preform can be cooled and then blown to the proper size in a second blow molding operation. Gartland et al., U.S. Pat. No. 4,463,121 teaches a polyethylene terephthalate polyolefin alloy having increased impact resistance, high temperature, dimensional stability and improved mold release. Ryder, U.S. Pat. No. 4,473,515 teaches an improved injection blow molding apparatus and method. In the method, a parison or preform is formed on a cooled rod from hot thermoplastic material. The preform is cooled and then transformed to a blow molding position. The parison is then stretched, biaxally oriented, cooled and removed from the device. Nilsson, U.S. Pat. No. 4,381,277 teaches a method for manufacturing a thermoplastic container comprising a laminated thermoplastic film from a preform. The preform has a thermoplastic layer and a barrier layer which is sufficiently transformed from a preformed shape and formed to a container. Jakobsen et al., U.S. Pat. No. 4,374,878 teaches a tubular preform used to produce a container. The preform is converted into a bottle. Motill, U.S. Pat. No. 4,368,825; Howard Jr., U.S. Pat. No. 4,850,494; Chang, U.S. Pat. No. 4,342,398; Beck, U.S. Pat. No. 4,780,257; Krishnakumar et al., U.S. Pat. No. 4,334,627; Snyder et al., U.S. Pat. No. 4,318,489; and Krishnakumar et al., U.S. Pat. No. 4,108,324 each teach plastic containers or bottles having preferred shapes or self-supporting bottom configurations. Hirata, U.S. Pat. No. 4,370,368 teaches a plastic bottle comprising a thermoplastic comprising vinylidene chloride and an acrylic monomer and other vinyl monomers to obtain improved oxygen, moisture or water vapor barrier properties. The bottle can be made by casting an aqueous latex in a bottle mold, drying the cast latex or coating a preform with the aqueous latex prior to bottle formation. Kuhfuss et al., U.S. Pat. No. 4,459,400 teaches a poly(ester-amid) composition useful in a variety of applications including packaging materials. Maruhashi et al., U.S. Pat. No. 4,393,106 teaches laminated or plastic containers and methods for manufacturing the container. The laminate comprises a moldable plastic material in a coating layer. Smith et al., U.S. Pat. No. 4,482,586 teaches a multilayer of polyester article having good oxygen and carbon dioxide barrier properties containing a polyisophthalate polymer. Walles, U.S. Pat. Nos. 3,740,258 and 4,615,914 teaches that plastic containers can be treated, to improve barrier properties to the passage of organic materials and gases such as oxygen, by sulfonation of the plastic.
Further, we are aware that the polyester has been developed and formulated to have high burst resistance to resist pressure exerted on the walls of the container by carbonated beverages. Further, some substantial work has been done to improve the resistance of the polyester material to stress cracking during manufacturing, filling and storage.
Beverage manufacturers have long searched for improved barrier material. In larger part, this research effort was directed to carbon dioxide (CO.sub.2) barriers, oxygen (O2) barriers and water vapor (H.sub.2 O) barriers. More recently original bottle manufacturers have had a significant increase in sensitivity to the presence of beverage extractable or beverage soluble materials in the resin or container. This work has been to improve the bulk plastic with polymer coatings or polymer laminates of less permeable polymer to decrease permeability. However, we are unaware of any attempt at introducing into bulk polymer resin or polyester material of a beverage container, an active complexing compound to improve barrier properties or to trap water soluble material to prevent their extraction or elution into the carbonated beverage.
Even with this substantial body of technology, substantial need has arisen to develop biaxially oriented thermoplastic polymer materials for beverage containers that can substantially reduce the passage of permeants in the extractable materials that pass into beverages intended for human consumption.